Versatile template-directed synthesis of gold nanocages with a predefined number of windows

Highly symmetrical gold nanocages can be produced with a controllable number of circular windows of either 2, 3, 4, 6 or 12 via an original fabrication route. The synthetic pathway includes three main stages: the synthesis of silica/polystyrene multipod templates, the regioselective seeded growth of a gold shell on the unmasked part of the silica surface and the development of gold nanocages by dissolving/etching the templates. Electron microscopy and tomography provide evidence of the symmetrical features of the as-obtained nanostructures. The optical properties of nanocages with 4 and 12 windows were measured at the single particle level by spatial modulation spectroscopy and correlated with numerical simulations based on finite-element modeling. The new multi-step synthesis approach reported here also allows the synthesis of rattle-like nanostructures through filling of the nanocages with a guest nano-object. With the potential to adjust the chemical composition, size and geometry of both the guest particle and the host cage, it opens new routes towards the fabrication of hollow nanostructures of high interest for a variety of applications including sensing devices, catalytic reactors and biomedicine.

Plasmonic gel nanocomposites for detection of high energy electrons

Radiation therapy is a common treatment modality employed in the treatment of cancer. High energy photons are the primary source of radiation but when administered, they leave an exit dose resulting in radiation damage to the adjacent healthy tissues. To overcome this, high energy electrons are employed in cases of skin cancer to minimize radiation induced toxicity. Despite these advances, measurement of delivered radiation remains a challenge due to limitations with existing dosimeters including labor intensive fabrication, complex read-out techniques and post-irradiation instability. To overcome these limitations, we have developed a novel colorimetric plasmonic gel nanocomposite for the detection of therapeutic levels of radiation delivered in electron beam therapy. The plasmonic nanocomposite consists of an agarose gel matrix encapsulating precursor gold ions, which are reduced to gold nanoparticles as a result of exposure to high energy electrons. The formation of gold nanoparticles renders a change in color to the agarose matrix, resulting in the formation of plasmonic gel nanocomposites. The intensity of the color formed exhibits a linear relation with the delivered electron dose, which can be quantified using absorbance spectroscopy. The plasmonic gel nanocomposites were able to detect doses employed in fractionated electron therapy, including in an anthropomorphic phantom used for planning radiation treatments in the clinic. Furthermore, the use of glutathione as a quenching agent facilitated qualitative and quantitative spatial mapping of the delivered dose. Our results indicate that the ease of fabrication, simplicity of detection and quantification using absorbance spectroscopy, determination of spatial dose profiles, and relatively low cost make the plasmonic gel nanocomposite technology attractive for detecting electron doses in the clinic.

Metal nanoparticles fabricated by green chemistry using natural extracts: biosynthesis, mechanisms, and applications

Nanoparticles (NPs) are new inspiring clinical targets that have emerged from persistent efforts with unique properties and diverse applications. However, the main methods currently utilized in their production are not environmentally friendly. With the aim of promoting a green approach for the synthesis of NPs, this review describes eco-friendly methods for the preparation of biogenic NPs and the known mechanisms for their biosynthesis. Natural plant extracts contain many different secondary metabolites and biomolecules, including flavonoids, alkaloids, terpenoids, phenolic compounds and enzymes. Secondary metabolites can enable the reduction of metal ions to NPs in eco-friendly one-step synthetic processes. Moreover, the green synthesis of NPs using plant extracts often obviates the need for stabilizing and capping agents and yields biologically active shape- and size-dependent products. Herein, we review the formation of metallic NPs induced by natural extracts and list the plant extracts used in the synthesis of NPs. In addition, the use of bacterial and fungal extracts in the synthesis of NPs is highlighted, and the parameters that influence the rate of particle production, size, and morphology are discussed. Finally, the importance and uniqueness of NP-based products are illustrated, and their commercial applications in various fields are briefly featured.

Holey Au-Ag alloy nanoplates with built-in hotspots for surface-enhanced Raman scattering

Plasmonic noble metal nanocrystals with interior nanogaps have attracted great attention in surface-enhanced Raman scattering (SERS) applications due to the presence of built-in hotspots. Herein, we report a synthesis route to holey Au-Ag alloy nanoplates by controlled galvanic replacement with Ag nanoplates as the sacrificial template, a sulfite-coordinated Au(i) salt as the Au source, and polyvinylpyrrolidone (PVP) as the capping agent. PVP helps regulate the anisotropic growth of nanopores on the Ag nanoplates to afford a highly holey nanostructure, and the monovalent Au(i) salt plays a critical role in stabilizing these holey nanoplates by rapidly enriching Au in the alloy nanostructures. Numerical simulations and experimental results suggest that these holey Au-Ag alloy nanoplates possess enormous internal hotspots for high sensitivity in the SERS analysis, and high stability for excellent reliability of the analysis under many harsh conditions. We believe that this strategy is potentially applicable to the synthesis of many other types of plasmonic nanostructures with inherent nanogaps for many sensing and imaging applications.

A Colorimetric Plasmonic Nanosensor for Dosimetry of Therapeutic Levels of Ionizing Radiation

Modern radiation therapy using highly automated linear accelerators is a complex process that maximizes doses to tumors and minimizes incident dose to normal tissues. Dosimeters can help determine the radiation dose delivered to target diseased tissue while minimizing damage to surrounding healthy tissue. However, existing dosimeters can be complex to fabricate, expensive, and cumbersome to operate. Here, we demonstrate studies of a liquid phase, visually evaluated plasmonic nanosensor that detects radiation doses commonly employed in fractionated radiotherapy (1-10 Gy) for tumor ablation. We accomplished this by employing ionizing radiation, in concert with templating lipid surfactant micelles, in order to convert colorless salt solutions of univalent gold ions (Au(1)) to maroon-colored dispersions of plasmonic gold nanoparticles. Differences in color intensities of nanoparticle dispersions were employed as quantitative indicators of the radiation dose. The nanoparticles thus formed were characterized using UV-vis absorbance spectroscopy, dynamic light scattering, and transmission electron microscopy. The role of lipid surfactants on nanoparticle formation was investigated by varying the chain lengths while maintaining the same headgroup and counterion; the effect of surfactant concentration on detection efficacy was also investigated. The plasmonic nanosensor was able to detect doses as low as 0.5 Gy and demonstrated a linear detection range of 0.5-2 Gy or 5-37 Gy depending on the concentration of the lipid surfactant employed. The plasmonic nanosensor was also able to detect radiation levels in anthropomorphic prostate phantoms when administered together with endorectal balloons, indicating its potential utility as a dosimeter in fractionated radiotherapy for prostate cancer. Taken together, our results indicate that this simple visible nanosensor has strong potential to be used as a dosimeter for validating delivered radiation doses in fractionated radiotherapies in a variety of clinical settings.

A hanging plasmonic droplet: three-dimensional SERS hotspots for a highly sensitive multiplex detection of amino acids

3D hotspots in a hanging plasmonic droplet result in an ultrahigh Raman Scattering for the ultratrace and multiplex identification of amino acids.

Fungal biosynthesis of gold nanoparticles: mechanism and scale up

Gold nanoparticles (AuNPs) are a widespread research tool because of their oxidation resistance, biocompatibility and stability. Chemical methods for AuNP synthesis often produce toxic residues that raise environmental concern. On the other hand, the biological synthesis of AuNPs in viable microorganisms and their cell-free extracts is an environmentally friendly and low-cost process. In general, fungi tolerate higher metal concentrations than bacteria and secrete abundant extracellular redox proteins to reduce soluble metal ions to their insoluble form and eventually to nanocrystals. Fungi harbour untapped biological diversity and may provide novel metal reductases for metal detoxification and bioreduction. A thorough understanding of the biosynthetic mechanism of AuNPs in fungi is needed to reduce the time of biosynthesis and to scale up the AuNP production process. In this review, we describe the known mechanisms for AuNP biosynthesis in viable fungi and fungal protein extracts and discuss the most suitable bioreactors for industrial AuNP biosynthesis.

Reversible synthesis of sub-10 nm spherical and icosahedral gold nanoparticles from a covalent Au(CN)2(-) precursor and recycling of cyanide to form ferric ferrocyanide for cell staining

A solution approach based on Au(CN)(2)(-) chemistry is reported for the formation of nanoparticles. The covalent character of the Au(CN)(2)(-) precursor was exploited in the formation of sub-10 nm nanospheres (≈2.4 nm) and highly monodisperse icosahedral Au nanoparticles (≈8 nm) at room temperature in a one-pot aqueous synthesis. The respective spherical and icosahedral Au morphologies can be controlled by either the absence or presence of the polymer polyvinylpyrrolidone (PVP). Using Au(CN)(2)(-) as a metal ion source, our findings suggest that the addition of citrate ions is necessary to enhance the particle formation rate as well as to generate a more homogeneous colloidal dispersion. Because of the presence of oxygen and the operation of a CN(-) etching process associated with Au(CN)(2)(-) complex formation, an interesting reversible formation-dissolution process was observed, which allowed us to repeatedly prepare spherical and icosahedral Au nanoparticles. Time-dependent TEM images and UV/Vis spectra were carefully acquired to study the reversibility of this formation-dissolution process. In view of the accompanying generation of toxic cyanide anions, we have developed a protocol to recycle cyanide in the presence of citrate ions through ferric ferrocyanide formation. After completion of particle formation, the residual solutions containing citrate ions and cyanide ions were processed to stain iron oxide nanoparticles endocytosized in cells. Additionally, the as-prepared 8 nm Au icosahedra could be isolated and grown to larger 57 nm-sized icosahedra using the seed-mediated growth approach.

Facile synthesis of gold nanorice enclosed by high-index facets and its application for CO oxidation

A facile method for generating Au nanorice enclosed by high-index facets in high purity. The nanorice shows much higher catalytic activity for CO oxidation than multiply twinned particles of Au enclosed by {111} facets at temperatures below 300 °C.

Simple electrochemical deposition of au nanoplates from au(I) cyanide complexes and their electrocatalytic activities

Nanostructured Au surfaces have unique and attractive properties as functional materials in many fields such as heterogeneous catalysis and electrocatalysis. Electrochemical deposition of Au has received much attention as a simple route for the fabrication of Au surface nanostructures. In this study, we report a simple electrodeposition of Au nanoplate structures from Au(CN)(2)(-) on Au surfaces in the absence of additives or premodification of electrode surfaces. The shape of the Au nanoplates as well as their surface structures is unique compared to other Au nanostructures electrodeposited from commonly employed AuCl(4)(-) complexes. The nanoplate Au surfaces exhibit unique electrocatalytic activities for oxygen reduction and glucose oxidation, which originate from the Au(110) and Au(100) facets present on nanoplate surfaces. A simple preparation of well-defined Au nanoplate structures would allow new opportunities in various areas utilizing Au-based substrates through further modification of Au surfaces.

Three-dimensional morphology and crystallography of gold nanorods

We determine the three-dimensional shape, to within 1 nm resolution, of single-crystal gold nanorods grown in the presence of silver ions using electron tomography and thickness profile measurements. We find that, contrary to the current literature, the octagonal side-facets are sparsely packed atomic planes all belonging to the same symmetry-equivalent family, {0 5 12}. Furthermore, the rod ends terminate in a pyramid with slightly different facets, and each pyramid is connected to the sides by four small {0 5 12} "bridging" facets.